Scanning optical unit

A scanning optical unit comprising:

• an acousto-optic modulating element including an acousto-optic modulating medium and a transducer which generates ultrasonic waves, and when a laser beam emitted from a laser light source passes through the acousto-optic modulating medium, the acousto-optic modulating element diffracts the laser beam by ultrasonic waves inputted by the transducer;
• main scanning/deflecting means for deflecting, in a main scanning direction of a recording medium, the laser beam which was diffracted by the acousto-optic modulating element;
• a reflecting mirror which is provided outside of an exposure region of the recording medium, and reflects the laser beam from the main scanning/deflecting means;
• and
• a sensor for determining a main scanning start position by receiving the laser beam reflected by the reflecting mirror,
• wherein a predetermined region of the recording medium is exposed by the laser beam deflected in a main scanning direction, and a distance, from a reflected position on the reflecting mirror of the laser beam received by the sensor to an exposure region side end portion of the reflecting mirror, is set on the basis of a distance to the transducer from an illuminated position of the laser beam which is a diffracted position of the laser beam within the acousto-optic modulating medium, a main scanning speed of the laser beam, and a propagation speed of ultrasonic waves within the acousto-optic modulating medium.

A scanning optical unit comprising:

• an acousto-optic modulating element including an acousto-optic modulating medium and a transducer which generates ultrasonic waves, and when a laser beam emitted from a laser light source passes through the acousto-optic modulating medium, the acousto-optic modulating element diffracts the laser beam by ultrasonic waves inputted by the transducer;
• a polygon mirror for deflecting, in a main scanning direction of a recording medium, the laser beam which was diffracted by the acousto-optic modulating element;
• a reflecting mirror which is provided outside of an exposure region of the recording medium, and reflects the laser beam from the polygon mirror;
• a sensor for determining a main scanning start position by receiving the laser beam reflected by the reflecting mirror;
• and
• an optical system containing an fθ lens,
• wherein a predetermined region of the recording medium is exposed by a laser beam deflected in the main scanning direction, and
• given that a focal length of the fθ lens is f, the main scanning speed which is the speed at which the laser beam moves on the recording medium is v, the distance between the reflecting mirror and an exposure surface of the recording medium is t, a distance from a reflection position on the reflecting mirror of the laser beam detected by the sensor to a recording medium side end portion of the reflecting mirror is l, a period of time from a time the laser beam reflected by the reflecting mirror is incident on the sensor to a time the acousto-optic modulating element is operated is τ, and a propagation speed of ultrasonic waves through the acousto-optic modulating medium at a time the acousto-optic modulating element is operated is V,
• adjustment is carried out such that a distance L from a diffraction position within the acousto-optic modulating medium to the transducer is L<V·[l·f/{v·(f−t)}−τ].

A scanning optical unit comprising:

• an acousto-optic modulating element including an acousto-optic modulating medium and a transducer which generates ultrasonic waves, and when a laser beam emitted from a laser light source passes through the acousto-optic modulating medium, the acousto-optic modulating element diffracts the laser beam by ultrasonic waves inputted by the transducer;
• a polygon mirror for deflecting, in a main scanning direction of a recording medium, the laser beam which was diffracted by the acousto-optic modulating element;
• a reflecting mirror which is provided outside of an exposure region of the recording medium, and reflects the laser beam from the polygon mirror;
• a sensor for determining a main scanning start position by receiving the laser beam reflected by the reflecting mirror;
• and
• an optical system containing an fθ lens,
• wherein a predetermined region of the recording medium is exposed by a laser beam deflected in the main scanning direction, and
• given that a focal length of the fθ lens is f, the main scanning speed which is the speed at which the laser beam moves on the recording medium is v, the distance between the reflecting mirror and an exposure surface of the recording medium is t, a propagation speed of ultrasonic waves through the acousto-optic modulating medium at a time the acousto-optic modulating element is operated is V, a period of time from a time the laser beam reflected by the reflecting mirror is incident on the sensor to a time the acousto-optic modulating element is operated is τ and a distance from a diffraction position within the acousto-optic modulating medium to the transducer is L,
• adjustment is carried out such that a distance l from a reflection position on the reflecting mirror of the laser beam detected by the sensor to a recording medium side end portion of the reflecting mirror is
• l>{(L/V)+τ}·{v·(f−t)/f}.

A scanning optical unit comprising:

• an acousto-optic modulating element including an acousto-optic modulating medium and a transducer which generates ultrasonic waves, and when a laser beam emitted from a laser light source passes through the acousto-optic modulating medium, the acousto-optic modulating element modulates an intensity of the laser beam by ultrasonic waves inputted by the transducer;
• main scanning/deflecting means for deflecting, in a main scanning direction of a recording medium, the laser beam whose intensity was modulated by the acousto-optic modulating element;
• an optical system including an fθ lens;
• a reflecting mirror which is provided outside of an exposure region of the recording medium, and reflects the laser beam from the main scanning/deflecting means;
• and
• a sensor for determining a main scanning start position by receiving the laser beam reflected at a predetermined position of the reflecting mirror,
• wherein the recording medium is scanned and exposed by said main scanning/deflecting means and said optical system including the fθ lens, and
• given that a focal length of the fθ lens is f, the main scanning speed which is the speed at which the laser beam moves on the recording medium is v, the distance between the reflecting mirror and an exposure surface of the recording medium is t, a distance from a reflection position on the reflecting mirror of the laser beam detected by the sensor to a recording medium side end portion of the reflecting mirror is l, a period of time from a time the laser beam reflected by the reflecting mirror is incident on the sensor to a time the acousto-optic modulating element is operated is τ, and a propagation speed of ultrasonic waves through the acousto-optic modulating medium at a time the acousto-optic modulating element is operated is V,
• adjustment is carried out such that a distance L from an intensity modulation position within the acousto-optic modulating medium to the transducer is
• L<V·[l·f/{v·(f−t)}−τ].

A scanning optical unit comprising:

• an acousto-optic modulating element including an acousto-optic modulating medium and a transducer which generates ultrasonic waves, and when a laser beam emitted from a laser light source passes through the acousto-optic modulating medium, the acousto-optic modulating element modulates an intensity of the laser beam by ultrasonic waves inputted by the transducer;
• main scanning/deflecting means for deflecting, in a main scanning direction of a recording medium, the laser beam whose intensity was modulated by the acousto-optic modulating element;
• an optical system including an fθ lens;
• a reflecting mirror which is provided outside of an exposure region of the recording medium, and reflects the laser beam from the main scanning/deflecting means;
• and
• a sensor for determining a main scanning start position by receiving the laser beam reflected at a predetermined position of the reflecting mirror,
• wherein the recording medium is scanned and exposed by said main scanning/deflecting means and said optical system including the fθ lens, and
• given that a focal length of the fθ lens is f, the main scanning speed which is the speed at which the laser beam moves on the recording medium is v, the distance between the reflecting mirror and an exposure surface of the recording medium is t, a propagation speed of ultrasonic waves through the acousto-optic modulating medium at a time the acousto-optic modulating element is operated is V, a period of time from a time the laser beam reflected by the reflecting mirror is incident on the sensor to a time the acousto-optic modulating element is operated is τ, and a distance from an intensity modulation position within the acousto-optic modulating medium to the transducer is L,
• adjustment is carried out such that a distance l from a reflection position on the reflecting mirror of the laser beam detected by the sensor to a recording medium side end portion of the reflecting mirror is
• l>{(L/V)+τ}·{v·(f−t)/f}.